Meters which determine the mass flow by measuring the Coriolis reaction force of a fluid within a conduit as developed in the 1950's included conduits which are rotated about a fixed axis. The rotation of the conduit creates a constant fluid reaction force couple against the conduit tubing. A rotational type meter is shown in Pearson, Pat. No. 2,624,198.
More recently developed Coriolis type flow meter structures utilize an oscillating or vibrating conduit drive system for creation of an alternating Coriolis reaction force by the fluid. A vibrational type meter structure is described in the Roth Pat. No. 2,865,201 and includes a generally circular conduit structure which is intended to simulate the rotational or gyroscopic type movement of the rotating conduit type meters.
Pat. Nos. 3,218,851; 3,261,205; and 3,329,019 to Sipin teach substantially straight conduits, oscillated perpendicular to the flow so as to produce the desired Coriolis reaction. There is minimal restriction of the flow within the relatively straight conduit tubing, with restriction being created only by the internal operating structure of the meter. However, these Sipin (and Roth, as referred to above) type meter structures are greatly limited in their ability to sense the Coriolis reaction.
A structural variation in vibrational or oscillatory type conduits, which is intended to increase the sensitivity of the meter, is described in Sipin's Pat. Nos. 3,355,944 and 3,485,098. The conduit structure in these patents introduces a deflection or displacement of the flow away from the typically straight line formed by the defined fluid stream or pipeline in which the flow meter is placed, and creates a substantially U-shaped conduit. The conduit tubing is vibrated at the point of maximum displacement which is located at the center of the U-shape. The maximum curvature of the U-shaped tubing in these patents is limited to 180.degree.. The Coriolis reaction force is measured on opposite sides of the imparted vibration on the leg portions of the U-shape.
Cox et al., Pat. No. 4,127,028, shows a cantilevered U-shaped conduit structure having rigidly mounted fixed input and output ends and including inwardly and outwardly extending bends on the leg portions of the U-shape. The U-shape is vibrated at its bight or projected end so as to create a cantilevered spring-like structure from its fixed mounting position. Additionally, a second similarly shaped conduit may be positioned adjacent to the first conduit creating a tuning fork effect when vibrated. The inwardly and outwardly extending bends on the leg portions of the conduit are included to increase the moment arm of the Coriolis reaction force on the U-shape about a deflection axis, which is defined within the patent text as being positioned at the symmetrical center line of the U-shape. The flow through each U-shaped portion of the conduit is parallel with a fluid particle making two complete loops between the input and output of the conduit. The joinder of the two loops or U-shaped portions is fixedly mounted adjacent the input and output of the conduit. The dual U-shaped conduit design of these patents creates substantial flow restriction by including numerous turns and reversals in the direction of flow as well as by requiring a perpendicular deflection of the flow direction at the input and output of the flow meter conduit from the pipeline or defined fluid stream.
FIG. 5 of the Cox '028 patent shows a projecting, substantially circular or spiraled loop having fixed input and output ends which are substantially coaxial with the pipeline feeding the flow into the conduit. This type mounting structure increases the flexibility of the tubing by increasing the tortional bending of the flow tube due to the combined effect of the applied oscillation and the Coriolis reaction. This type structure also limits flow restriction at the input and output ends of the conduit as well as utilizing gently curved tubing portions in directing the fluid flow through the conduit shape.
Pat. No. 4,491,025 to Smith utilizes a flow splitting manifold to eliminate the continuous double loop formation in the Cox '028 dual U-shaped tube design. The flow splitting manifold supplies substantially equivalent flow in the same direction to both U-shaped conduits. However, the flow into the conduit is directed in a 90.degree. turn from the direction of flow of a linear feed pipeline, thus, creating a flow restriction at the input and output ends.
Sipin Pat. No. 4,599,833 shows an S-shaped conduit having tight turns or curvature in its tubing formation so as to limit the lateral displacement of the conduit structure with respect to the axial line of the defined fluid stream. The conduit shape in this patent is also intended to increase the moment arms of the Coriolis reaction force with respect to the oscillatory motion, similar to the inward and outward bends in Cox '028, while limiting the size of the conduit structure. This structure, however, causes substantial flow restriction around the tight turns of the S-shaped tubing and also causes drastic reversal in the direction of flow within the conduit. A meter produced by the Smith Meter Company (the assignee of the Sipin '833 patent) utilizes an S-shaped conduit in which the turns in the direction of flow are gentler as compared to that shown ad by the Sipin '833 patent. This type structure eliminates the minimumal lateral displacement of the conduit as required by the patent. The S-shape portion of the Smith meter conduit is positioned substantially transverse to the line of the defined fluid stream; therefore, creating an initial restriction at the input and a corresponding restriction at the exhaust of the S-shape portion of the conduit.
A mass flow meter produced by the Danfoss Company of England includes two substantially parallel flow tubes which are positioned between opposite flow splitting manifolds. Each of the flow tubes is displaced slightly from the center line of the conduit (and the line formed by the defined fluid stream). Both flow tubes lie in a single plane so that the structure does not substantially form a projected dual U-tube configuration. The oscillatory driver is positioned at the center of the length with the Coriolis reaction being measured by sensing the twist in the opposing tubes with respect to one another.